Water jet has been employed in extraacton of minerals for many years but the applications of low pressure jent s ar emodfined to some fields. With increasing strength of equipment it is possible to consider the use of high speed water jets for cutting hard rock. The high speed water jet technology is applied to various engineering fiels such as precessing rocks, quarrying rocks, mechanical fracturing as wel as rock excavation under the sea. For slot cutting in rocks with high speed water jets it is necessary to establish the empirical formula for estiamation of the cutting depth. The cutting depth is influenced by cutting parameters such as driving pressure, traverse speed, standoff distance, and shape and diameter of nozzel. Tests were carried out with a variety of cutting parameters on three types of granite. Nozzle pressures ranged from 1,200 to 2,800 bar, traverse speeds from 0.45 to 10.38 cm/min, standoff distances from 4.5 to 13.5 mm, and three types of nozzle diameter were used.